KR102199425B1 - Electro-optic device - Google Patents

Abstract

It provides an electro-optical device capable of increasing the current supplied to the sense line. Between the power supply ELVDD and the anode of the OLED 10, a driving transistor 11 to which a reset voltage or a gradation voltage is applied to the gate is electrically connected. The drain of the initialization transistor 14 for selectively supplying the reference voltage Vref is electrically connected to the connection point between the drain of the driving transistor and the anode of the OLED, and a sensing transistor 16 electrically connected to the power supply and the voltmeter. The gate of) is electrically connected.

Description

Electro-optical device {ELECTRO-OPTIC DEVICE}

The present invention relates to an electro-optical device for driving an electro-optical device using a current-emitting element that emits light by electric current.

Recently, an electro-optical device comprising an organic EL device (Organic Electroluminescence Light Emitting Diode) (OLED) that emits light at an intensity according to the supplied current has been developed. In such an electro-optical device, the amount of current supplied to the OLED is determined by the gray level in the image signal. By controlling the amount of current supplied to each OLED for each color based on the data, a full color image is displayed, but since the light emitting layer is generated from an organic compound, the degree of time degradation is normal silicon semiconductor It is larger than a light-emitting element composed of, and has a problem in that the current-luminance characteristics of each OLED change due to deterioration with time, thereby impairing the reproducibility of the original image. Although it emits brighter light, the reproducibility of the original image is greatly impaired because there is a variation in the aging deterioration that occurs in each OLED due to various factors. The image reproducibility due to the change in the current-luminance characteristic is greatly damaged. The deterioration of the above can be compensated by adjusting the conversion coefficient from the video signal to the current value based on the luminance of each OLED.

However, it is practically difficult to directly measure the change in the luminance value of each OLED.

Here, the current value supplied to each OLED is already known, and when the deterioration of the OLED over time occurs, the voltage-current characteristics of the OLED also fluctuate, and a certain correlation exists between the two. It has been conventionally proposed to measure the anode voltage of the OLED, predict the change in the current-luminance characteristic due to aging deterioration based on the measured anode voltage, and adjust the conversion coefficient based on the predicted current-luminance characteristic. Yes (for example, Patent Documents 1, 2, and 3).

Japanese Patent No. 4593868 Japanese Patent No. 4877261 Japanese Patent No. 4530017

In the techniques described in Patent Documents 1 to 3, the voltage of the anode terminal of each OLED was directly measured by a voltmeter connected in parallel between the anode terminal of each OLED and the ground.

However, since the current value supplied to each OLED is inherently small, there is a problem with this method of measuring voltage, i.e., the voltage at the terminal of the voltmeter connected in parallel with the OLED is the same voltage as the anode terminal of the OLED, connecting both. Since the parasitic capacitance generated in the wiring (sense line) has been saturated, a part of the current supplied to the OLED is branched to the sense line, and if the parasitic capacitance of the sense line is not stopped charging, the voltmeter will display the voltage at the anode terminal of the OLED. However, since the current value supplied to the OLED is several µA or less even at the time of maximum luminance display, the current branching to the sense line is inevitably small, so the time before charging and discharging the parasitic capacitance of the sense line It takes. Therefore, according to the conventional technique, since it is not possible to measure a voltage having a good response, the compensation of image reproducibility by adjusting the transform coefficient cannot be performed with good response.

In addition, as described above, if the current supplied to the sense line is originally small, the potential of the sense line is easily affected by noise, so the voltage of the sense line fluctuates due to noise from outside or inside the panel, resulting in sufficient measurement accuracy. There is also a problem that can not be obtained. The problem caused by the small current as described above becomes remarkable because the sensing line becomes longer as the size of the panel increases. In addition, multiple measurements at different luminances are required to more accurately predict the change in current-luminance characteristics, but the smaller the gradation becomes, the smaller the current value supplied to the OLED, so the problem caused by the small current is remarkable. do.

In addition, in order to avoid the above problem from becoming noticeable when the luminance is small, it is also possible to prepare a sensing-only image that does not contain a low luminance image signal, rather than a normal image that can receive a low luminance image signal. I can think. However, in that case, since the sensing-only image cannot be displayed while the normal image is being displayed, the measurement of the anode voltage of each OLED is limited to when the display panel is started up and when the display panel is shut down.

Here, it is an object of the present invention to increase the current supplied to the voltmeter through the sense line, and as a result, regardless of the panel size or luminance, the exact voltage of the electrode of each light emitting element to charge the sense line It is an object to provide an electro-optical device in which the time during which the measurement cannot be performed can be extremely short, and the voltage of the electrode of each light emitting element can be measured even during normal image display.

The electro-optical device according to the present invention is an electro-optical device that emits light with a luminance corresponding to the gradation data by supplying a driving current corresponding to a gradation voltage based on the input gradation data to a light emitting element. And an electrode of the light emitting element, the gray voltage is selectively applied to the gate, and when the gray voltage is applied to the gate, a driving current corresponding to the applied gray voltage is supplied to the light emitting element A second transistor having a gate electrically connected to the electrode of the light emitting element and a source or a drain electrically connected to a circuit including a voltmeter, and the gate of the first transistor. In a state in which a gray voltage is applied, a control circuit for reading a measurement value of the voltmeter and correcting the gray voltage applied to the gate of the first transistor based on the measured value is provided. do.

According to the present invention, since the current flowing through the sense line is controlled by the second transistor whose gate is electrically connected to the electrode of the light emitting element, the current supplied to the sense line can be increased. Therefore, according to the present invention, it is possible to extremely shorten the time in which the voltage of the electrode of each light emitting element cannot be accurately measured to charge the sense line, regardless of the panel size or luminance, and even during normal image display, each light emission It becomes possible to measure the voltage of the electrode of the device. In addition, "electrically connected" means that the elements are directly connected, but are connected through other elements (transistors, diodes, etc.).

1 is a block diagram showing a schematic circuit configuration of a first embodiment.
Fig. 2 is a detailed circuit diagram of a driving circuit for each OLED constituting a pixel circuit.
3 is a detailed circuit diagram of a voltage detector.
4 is a flowchart showing the processing contents of the control circuit.
5 is a flowchart showing the processing contents of the control circuit.
6 is a timing chart showing the transition of signals applied to the driving circuit by the control circuit.
7 is a circuit diagram showing the state of the driving circuit in S001.
8 is a circuit diagram showing the state of the driving circuit in S002.
9 is a circuit diagram showing the state of the driving circuit in S003.
10 is a circuit diagram showing the state of the driving circuit in S004.
11 is a circuit diagram showing the state of the driving circuit in S005.
12 is a circuit diagram showing the state of the driving circuit in S006.
13 is a circuit diagram showing the state of the driving circuit in S006.
14 is a circuit diagram showing the state of the driving circuit in S007.
15 is a circuit diagram showing the state of the driving circuit in S008.
16 is a graph showing a correlation between current-voltage characteristics and current-luminance characteristics of OLED.
17 is a detailed circuit diagram showing a modified example of the voltage detector.
18 is a graph showing the temperature dependence of OLED.
19 is a graph for explaining the object of the second embodiment.
20 is a flowchart showing the processing contents of the control circuit.
21 is a flowchart showing the processing contents of the control circuit.
22 is a flowchart showing the processing contents of the control circuit.
23 is a circuit diagram showing the state of the driving circuit in S104.
24 is a graph for explaining the operation of the second embodiment.
Fig. 25 is a detailed circuit diagram of a driving circuit for each OLED constituting the pixel circuit of the third embodiment.
26 is a detailed circuit diagram of a drive circuit for each OLED constituting the pixel circuit of the fourth embodiment.

Hereinafter, an electro-optical device according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the embodiment shown below is an example of embodiment of this invention, and this invention is not limited to these embodiment.

(First embodiment)

An electro-optical device according to a first embodiment of the present invention will be described in detail with reference to the drawings.

1 is a block diagram showing the configuration of an electro-optical device according to a first embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific circuit configuration of each pixel circuit 1.

The electro-optical device consists of three sets of OLEDs for each pixel constituting the display panel (to express full color, three sets of OLEDs each emitting each primary color (red, green, and blue) with a set gradation) (10) is provided. In Fig. 1, a set of driving circuits for each OLED 10 is referred to as "pixel circuit 1". In addition, in the pixel circuit 1, driving circuits of a plurality of OLEDs 10 constituting each pixel are arranged in a matrix shape to constitute a display panel, and as shown in FIG. 2, a plurality of OLEDs arranged in the column direction A common data line (D) is connected to the driving circuit of (10), and a common first scanning line (S1) and a common second scanning line (S2) are connected to the driving circuits of the plurality of OLEDs 10 arranged in the row direction. , A common compensation transistor drive line (C), a common initialization transistor drive line (N), and a common light emitting switch drive line (E) are connected, and a first power line ( P) and the second power supply line W are connected. Further, to the above-described first power supply line P, a power supply having a constant voltage ELVDD sufficiently high compared to the earth potential is supplied from a power supply circuit (not shown), and the second power supply line W is It is connected to a sufficiently low voltage (VSS) power supply. In addition, the cathode of each OLED 10 is connected to earth.

And, as shown in FIG. 1, the electro-optical device according to the first embodiment is constituted by such a pixel circuit 1 and a control circuit 2.

The control circuit 2 receives an image signal consisting of gray level data for each primary color supplied from the outside, and supplies a gray level voltage for setting the luminance of each OLED 10 to the above-described data line D, This is a circuit that supplies a scan signal to the first and second scan lines S1 and S2 described above. Specifically, the control circuit 2 has a processor (computer) that operates according to the firmware stored in the storage medium 3, and by operating according to the firmware, therein, in the control circuit 2, other than the processor By cooperating with the hardware of the gradation data correction operation unit 21, the gradation voltage generation unit 22, the reference voltage supply circuit 23, the voltage detection unit 24, and each function of the scan signal generation unit 25 is generated. .

The reference voltage supply circuit 23 is a reset voltage (Voff, provided, Voff = for resetting the driving circuit of the OLED 10 connected to the data line D, respectively, to each of the above-described data lines D). ELVDD) and a reference voltage for voltage measurement (Vref, provided that Vth_el>Vref≥ELVDD (Vth_el is the emission threshold voltage of the OLED)) are supplied.

Further, the gradation voltage generation unit 22 generates gradation voltages to be set for each OLED 10 based on gradation data for each primary color of each pixel, and corrects it by the gradation data correction operation unit 21 as described later. , For each column of the OLED 10, the generated gradation voltage Vdata is sequentially supplied from the one for the OLED 10 in the first row to the corresponding data line D.

In addition, the scan signal generator 25 is a first scan signal that designates a driving circuit of the OLED 10 to which the gray voltage Vdata sequentially supplied from the gray voltage generator 22 to each data line D is to be set. (Scan1) is supplied to the first scanning line S1. Further, the scan signal generation unit 25 supplies a second scan signal Scan2 specifying a row of the OLED 10 on which voltage measurement is to be performed to the second scan line S2. In addition, the scan signal generation unit 25 drives the compensation transistor driving signal GCOM to each compensation transistor driving line C, the initialization transistor driving signal GINT to each initialization transistor driving line N, and driving each light-emitting switch. Light-emitting switch drive signals EM are supplied to line E, respectively.

Further, the voltage detector 24 measures the anode voltage of the OLED 10 in the row designated by the second scan signal Scan2 through each data line D. Here, the voltage detector 24 reads the measured anode voltage from the voltmeter 241 wired as shown in FIGS. 2 and 3. That is, each data line D is branched as shown in FIG. 2, and an output terminal for the gradation voltage generator 22, an output terminal for the reference voltage supply circuit 23, and a voltage detection circuit 24 A voltmeter 241 for use is connected in parallel. Further, the voltmeter 241 is connected in parallel with the constant current source 242.

In addition, for each OLED 10, the gradation data correction operation unit 21 is based on the anode voltage at the time of application of the reference voltage measured by the voltage detection unit 24 and the anode voltage at the time of application of the gradation voltage for each OLED 10 (the gradation The gradation voltage generator 22 predicts the deviation from gradation data of the luminance of the OLED 10 at the time of voltage application, and corrects (feeds back) the gradation data to compensate for the deviation according to the predicted degree of deterioration. ).

Next, referring to Fig. 2, the circuit configuration of the driving circuit of each OLED 10 will be described. Between the power supply line P and the anode of the OLED 10, the driving transistor 11 (corresponding to the first transistor) and the light emitting switch transistor 12 are connected in series in order. Further, a light emitting switch driving line E is electrically connected to the gate of the light emitting switch transistor 12. Further, between the gate and the drain of the driving transistor 11, the compensation transistor 13 is electrically connected, and the gate of the compensation transistor 13 is electrically connected to the compensation transistor driving line C. In addition, an initialization transistor 14 (equivalent to the third transistor) is electrically connected between the connection point between the drain of the driving transistor 11 and the source of the light emitting switch transistor 12 and the data line D. In addition, the gate of the initialization transistor 14 is electrically connected to the initialization transistor driving line N. Further, between the source and the gate of the driving transistor 11, the first capacitor 31 and the second capacitor 32 are connected in series in order from the gate side. The first scan transistor 15 is electrically connected between the connection point of the capacitors 31 and 32 and the data line D, and the gate of the first scan transistor 15 is the first scan line S1 It is electrically connected to.

Further, between the data line D and the second power line W, the sensing transistor 16 and the second scan transistor 17 are electrically connected sequentially from the data line D side. And, the gate of the sensing transistor 16 (equivalent to the second transistor) is electrically connected to the anode of the OLED 10, and the gate of the second scanning transistor 17 is electrically connected to the second scanning line S2. Has been.

Further, each of the transistors 11 to 17 constituting the driving circuit is a P-channel MOSFET.

Next, using the flowcharts of Figs. 4 and 5, the timing charts of Figs. 6, and the circuit diagrams of Figs. 7 to 15, the control contents of the driving circuits of the OLEDs 10 by the control circuit 2 will be described. do.

The processing shown in the flowcharts of FIGS. 4 and 5 may be executed every time an image of one frame is displayed on the display panel of the electro-optical device, for example, or may be executed only when the display panel is started up or shut down. In the former case, the processing shown in the flowcharts of Figs. 4 and 5 may be executed for all rows of the OLED 10 whenever an image of one frame is displayed on the display panel, or only for a specific row of the OLED 10. It is executed, but it can also be configured to shift the row to be executed row by row.

In any case, the process starts and in the first S001, the control circuit 2 sets the potential of the first scan signal Scan1 to L (first scan transistor 15 = ON), and the compensation transistor drive signal GCOM. The potential of L (compensation transistor 13 = ON), the potential of the initialization transistor driving signal GINT is L (initialization transistor 14 = ON), and the potential of the light emitting switch driving signal EM is H (light emitting switch transistor (12) = OFF), with the potential of the second scan signal Scan2 set to H (the second scan transistor 17 = OFF), by applying the reset voltage Voff to all data lines D , The driving transistors 11 of the driving circuits of all the OLEDs 10 are turned off, respectively (see Fig. 7). This is to prevent a short circuit between the power supply of ELVDD and the power supply of the reference voltage Vref in the next step S002 (Fig. 8).

In the following S002, the control circuit 2 sets the potential of the first scan signal Scan1 to H (first scan transistor 15 = OFF) and the potential of the compensation transistor driving signal GCOM to H (compensation transistor 13). =OFF), by switching the potential of the light emitting switch driving signal EM to L (light emitting switch transistor 12 = ON), and switching the potentials of all data lines D to the reference voltage Vref, the second capacitor ( By maintaining the reset voltage Voff at 32), the driving transistor 11 is kept OFF, and the reference voltage Vref is applied to the anodes of all the OLEDs 10 in the row to be executed (see FIG. 8). ). From the conditions of the reference voltage Vref described above, the OLED 10 does not emit light at this point in time.

In the following S003, the control circuit 2 sets the potential of the initialization transistor driving signal GINT to H (initialization transistor 14 = OFF) and the potential of the light emitting switch driving signal EM to H (light emitting switch transistor 12) = OFF), the potential of the second scan signal Scan2 is switched to L (second scan transistor 17 = ON), and the reference voltage Vref is separated from all data lines D, and each data line ( By connecting the voltage detectors 24 to each of D), the reference voltage Vref is maintained in the internal capacities of all the OLEDs 10 in the row to be executed (Fig. 9). In this way, current flows from the constant current source 242 to the power supply of VSS through the sensing transistor 16 and the second scanning transistor 17, but the reference voltage Vref applied to the gate of the sensing transistor 16 Since the current value I becomes constant regardless of the impedance between the source and the drain corresponding to, the voltage value Vsense measured by the voltmeter 241 is as shown in Equation 1 below.

However, Vth here is a threshold value of the voltage between the gate and source of the sensing transistor 16, I is the current value of the constant current source 242, and β is a coefficient representing the characteristics of the sensing transistor 16. This voltage value Vsense corresponds to the first measured value.

In the following S004, the control circuit 2 sets the potential of the first scan signal Scan1 to L (first scan transistor 15 = ON), and the potential of the second scan signal Scan2 to H (second scan transistor ( 17) = OFF), and by applying the reference voltage Vref to all the data lines D, the driving transistors 11 of the driving circuits of all the OLEDs 10 in the execution target row are initialized (Fig. 10). ). In the next step S005 (FIG. 11), in order to compensate the Vth of the driving transistor 11, the gate-source voltage Vgs of the driving transistor 11 is set to a sufficiently low value and the driving transistor 11 ) To ON. As a result, the voltage held by the second capacitor 32 becomes the reference voltage Vref, the reference voltage Vref is applied to the gate of the driving transistor 11, and the driving transistor 11 is turned ON.

In the next S005, the control circuit 2 switches the potential of the compensation transistor driving signal GCOM to L (compensation transistor 13 = ON), and the driving transistor 11 and the compensation transistor from the first power line P 13) to generate a current passing through (see Fig. 11). As a result, the gate voltage of the driving transistor 11 of the driving circuit of all the OLEDs 10 in the execution target row gradually rises from the reference voltage Vref, and ELVDD-Vth (where Vth is the driving transistor ( 11) and is held in the first capacitor 31. That is, the driving transistor 11 is diode-connected and Vth is programmed.

In the following S006, the control circuit 2 switches the potential of the compensation transistor driving signal GCOM to H (compensation transistor 13 = OFF), and first scan signals other than the first row (Scan1 to n). Is switched to H (first scan transistor 15 = OFF) (refer to Fig. 12), and at the same time, the gradation voltage Vdata for the OLED 10 in the first row is applied to the data line D (Fig. 13 Reference). After that, the first scan signal (Scan1 to n) is shifted one row at a time to L (first scan transistor 15 = ON), and in synchronization with this, the OLED of each row is applied to the data line D. (10) The gradation voltage (Vdata) for use is sequentially applied. As shown in Fig. 13, in the row in which the first scan signals Scan1 to n are switched to L (first scan transistor 15 = ON), in the driving circuit of the OLED 10, through the data line D. The gradation voltage Vdata is applied to the connection point of the first capacitor 31 and the second capacitor 32, and the potential of the connection point rises from Vref to Vdata. In this way, due to the capacitance coupling through the first capacitor 31, the gate voltage of the driving transistor 11 is shifted by an increase (Vdata-Vref) of the potential of the connection point, and becomes ELVDD-Vth+Vdata-Vref. do. As a result, the gate-source voltage Vgs of the driving transistor 11 becomes Vgs=Vdata-Vref-Vth. As shown in Fig. 12, in the row in which the first scan signals Scan1 to n are switched to H (first scan transistor 15 = OFF) after the gradation voltage is programmed, the driving circuit of the OLED 10 Since the one scan transistor 15 is turned off and the connection point of the first capacitor 31 and the second capacitor 32 is floated, the Vgs is held, thereby completing the programming of the gradation voltage. Further, the value of the gradation voltage is a value obtained by multiplying the luminance value of gradation data input to the control circuit 2 by a predetermined conversion factor and further executing the gradation correction function. However, since the coefficient of the gradation correction function is "1" at the time when the processing in Fig. 4 is first executed, the gradation voltage is not corrected. In addition, when the processing of Figs. 4 and 5 is executed during startup or shutdown, since grayscale data input to the control circuit 2 from the outside does not exist, grayscale data having a predetermined luminance value (Voled measurement Data), a gradation voltage is calculated. And, at the time of completion of S006, all data lines D are disconnected from the terminals of the gradation voltage generator 22.

In the following S007, the control circuit 2 switches the potential of the light emitting switch driving signal EM in all rows to L (light emitting switch transistor 12 = ON), and drives all OLEDs 10 corresponding to each. A current proportional to the programmed gradation voltage (Vgs=Vdata-Vref-Vth) is supplied to the driving transistor 11 of the circuit (Fig. 14). In this way, each OLED 10 emits light with a luminance corresponding to the value of the current supplied to each according to each current-luminance characteristic. The voltage of the anode of each OLED 10 at this time is the voltage to be measured (Voled).

In the following S008, the control circuit 2 switches the potential of the second scan signal Scan2 to L (second scan transistor 17 = ON) (Fig. 15). In this way, current flows from the constant current source 242 to the power supply of VSS through the sensing transistor 16 and the second scanning transistor 17. Since the current value I is constant regardless of the impedance between the source and the drain corresponding to the measurement target voltage Voled applied to the gate of the sensing transistor 16, the voltage value Vsense' measured by the voltmeter 241 is ) Is as shown in Equation 2 below.

However, the meaning of each integer in Equation 2 is the same as in Equation 1 described above. This voltage value Vsense' corresponds to the second measured value.

In the following S009, the control circuit 2 sets the potential of the first scan signal Scan1 to L (first scan transistor 15 = ON) and the potential of the compensation transistor driving signal GCOM to L (compensation transistor 13). =ON), the potential of the initialization transistor driving signal GINT is set to L (initialization transistor 14 = ON), the potential of the light emitting switch driving signal EM is set to H (light emitting switch transistor 12 = OFF), the second scan The potential of the signal Scan2 is switched to H (the second scanning transistor 17 = OFF), and by applying the reset voltage Voff to all the data lines D, all the OLEDs 10 emit light. (See Fig. 7).

In the following S010, the control circuit 2 calculates Voled by subtracting the Vsense measured in S003 from the Vsense measured in S008 and adding a known Vref as shown in Equation 3 below.

In the following S011, the control circuit 2 compares the Voled calculated in S010 with the Voled (reference value) in the current (Ioled1) corresponding to the Vgs (=Vdata-Vref-Vth) calculated at the time of shipment. The difference (ΔV) of is calculated. In addition, since there is no deterioration at the time when the processing in Figs. 4 and 5 is first executed, ΔV = 0.

In the following S012, the control circuit 2 determines the current-luminance characteristic after deterioration corresponding to ?V. Here, there is a correlation between the change in the voltage-current characteristic and the change in the current-luminance characteristic due to deterioration of the OLED 10. That is, the voltage-current characteristic curve shifts toward the side where the voltage increases in the voltage axis, and the current-luminance characteristic straight line is inclined in the direction in which the luminance increases. And, between the shift amount in the former and the change amount of the inclination angle in the latter, there is a correlation that can be expressed by an equation. Therefore, the control circuit 2 can calculate the amount of change from the inclination angle before the deterioration of the current-luminance characteristic straight line after deterioration based on ?V. For example, the solid line shown in Fig. 16B is a voltage-current characteristic curve before deterioration, and the voltage-current characteristic curve shifts to a position indicated by a dotted line due to deterioration. At this time, without performing gradation correction on the predetermined gradation data, the calculated gradation voltage (Vgs=Vdata-Vref-Vth) is applied to the gate of the driving transistor 11, and accordingly the driving transistor 11 When Ioled1) is supplied to the OLED 10, the calculated Voled is Voled1 (reference value) before deterioration and becomes Voled2 after deterioration. That is, ΔV = Voled2-Voled1, and indicates the amount of shift of the voltage-current characteristic curve. On the other hand, the solid line shown in Fig. 16(a) is referred to as the current-luminance characteristic line before deterioration, and the current-luminance characteristic line is inclined to an angle indicated by the dotted line due to deterioration. At this time, the luminance of the OLED 10 to which the current Ioled1 was supplied is L1 before deterioration, and L2 after deterioration. Accordingly, after deterioration, when the current Ioled2 is supplied to the OLED 10, the OLED 10 can emit light with the original luminance corresponding to the gray scale data. Here, the control circuit 2 can determine the value Ioled2 of the current to be supplied to the driving transistor from the deteriorated current-luminance characteristic straight line corresponding to ?V and the original luminance indicated by the gradation data.

Here, in the following S013, the control circuit 2 determines the correction relationship of Ioled based on the difference in the slope of the current-luminance characteristic before and after deterioration. This correction relationship can be expressed as a ratio because the degradation of the OLED is represented by the difference in the slope of the current-luminance characteristic.

In the following S014, the control circuit 2 determines the gradation correction function described above based on the correction relationship determined in S013.

In the following S015, the control circuit 2 calculates the grayscale data of the next frame (when the processing in Figs. 4 and 5 is executed only at the start-up, all of the grayscale data input later), to the above-described conversion coefficient. As a result, the conversion to the gradation voltage and correction based on the gradation correction function determined in S014 are performed. In addition, when the execution target row is one row at a time, the gradation voltage is corrected for the execution target row based on the gradation correction function determined in S014 during the processing of Figs. 4 and 5 this time, and for rows other than the execution target row, If there is a gradation correction function determined in S014 during the processing of Figs. 4 and 5 performed in the past, the gradation voltage is corrected based on the gradation correction function stored in a memory (not shown). Otherwise, the correction is performed. Do not do. After completion of S015, the control circuit 2 ends the entire process of FIGS. 4 and 5.

According to the first embodiment configured as described above, since the wiring branched from the anode of the OLED 10 is electrically connected to the gate of the sensing transistor 16, the time required for charging to the wiring is problematic. It doesn't work. Further, since the current supplied to the voltmeter 241 of the voltage detection unit 24 is supplied by the constant current source 242, it can be made much larger than the current supplied to the OLED 10. Therefore, since the sense line connected to the voltmeter 241 is immediately charged, the voltage measurement is completed in a short time and the measured voltage does not fluctuate due to noise.

<modification example>

In the first embodiment described above, the constant current source 242 may be omitted as the configuration of the voltage detection unit 24 is shown in FIG. 17. However, in this case, it is necessary to make Vss sufficiently lower than Vref. As a result, the Vsense measured in S003 (FIG. 9) is as shown in Equation 4 below, and the Vsense measured in S008 (FIG. 15) is as shown in Equation 5 below.

의 요소가 포함되지 않는다. 무엇보다도, S010에서 수학식 3을 실행함으로써, I 및 β의 관계없이, Voled를 산출할 수 있다는 것에는 변함이 없다.As shown in these Equations 4 and 5, in Vsense and Vsense',

The element of is not included. Above all, there is no change in that by executing Equation 3 in S010, Voled can be calculated regardless of I and β.

(Embodiment 2)

Next, with reference to Figs. 18 to 24, a second embodiment of the present invention will be described. In the second embodiment, in correcting the gradation voltage caused by the aging deterioration of the OLED, taking into account the change in the characteristic due to the temperature rise of the OLED, it is to obtain the amount of change in the current-voltage characteristic due to the aging deterioration. , Is characterized.

As shown in Fig. 18, it is known that the current-voltage characteristic of the OLED 10 has a temperature dependence, and when it is lower than normal temperature, it shifts to the high voltage side along the voltage axis, and when it is higher than normal temperature, it shifts to the low voltage side. Further, since the OLED 10 has heat due to self-heating or heat generated by the driving transistor 11, it is likely to be affected by changes in current-voltage characteristics caused by temperature. Therefore, since the change in the anode voltage of the OLED 10 contains a component due to deterioration over time and a component due to temperature change, detecting the change in anode voltage identifies both components and is due to deterioration over time. There is a problem that compensation cannot be performed based only on the amount of change in the voltage-current characteristic to be performed.

For example, the solid line shown in Fig. 19B is a voltage-current characteristic curve at room temperature, and when it becomes high temperature, the voltage-current characteristic curve shifts to a position indicated by a dashed-dotted line. At this time, without performing gradation correction on predetermined gradation data, the calculated gradation voltage (Vgs=Vdata-Vref-Vth) is applied to the gate of the driving transistor 11, and accordingly, the corresponding driving transistor 11 When Ioled1) is supplied to the OLED 10, the calculated Voled is Voled1 at room temperature and Voled2 at high temperature. Here, since the above-described reference value is Voled1 measured at room temperature when shipped from the factory, when Voled2 is measured at high temperature, a negative value of ΔV is calculated, and based on this, the control circuit 2 generates a current due to deterioration over time. -In consideration of the voltage characteristic, the current-luminance characteristic, and the correlation, the current-luminance characteristic straight line indicated by the broken line in Fig. 19(a) is predicted as after deterioration. However, since the current-luminance characteristic of the OLED 10 does not change due to temperature change, in this case, correction of the gradation voltage based on the change in the current-luminance characteristic should not be performed. Regardless of this, if the control circuit 2 corrects the gradation voltage based on the predicted current-luminance characteristic line and supplies Ioled2 to the OLED 10, the luminance of the OLED 10 becomes L3. to be.

In order to discriminate such a change in current-voltage characteristic due to temperature change from change in current-voltage characteristic due to deterioration over time, in the second embodiment, temperature dependence on the leakage current when the driving transistor 11 is turned off. Focusing on the existence of this, the leakage current is used to measure the temperature, and the amount of change in the current-luminance characteristic due to the temperature change is calculated.

In the second embodiment, since the circuit configuration of the electro-optical device is the same as that of the first embodiment described above, a description thereof is omitted.

Using the flowcharts of Figs. 20 to 22 and the circuit diagrams of Figs. 7 to 1 5 and 23, control contents for the driving circuit of each OLED 10 by the control circuit 2 of the second embodiment are described. , Explain.

The processing shown in the flowcharts in Figs. 20 to 22 starts at the same timing as in the first embodiment. Then, the control circuit 2 starts the processing and executes the same processing as S001 to S003 in Fig. 4 in the first S101 to S103.

In the following S104, the control circuit 2 switches the potential of the light-emitting switch drive signal EM to L (light-emitting switch transistor 12 = ON) (see Fig. 23). At this time, although the driving transistor 11 remains OFF, a leak current in proportion to the temperature is passed and supplied to the OLED 10 through the light emitting switch transistor 12. As a result, the anode voltage of the OLED 10 becomes a value (Vtemp) obtained by dividing the potential difference between ELVDD and ELVSS by the impedance between the source and the drain of the driving transistor 11 and the impedance of the OLED 10. Here, the control circuit 2 accepts Vtemp measured by the voltmeter 241 at a timing at which Vtemp is stable in a steady state.

Subsequently, in S105 to S110, the control circuit 2 executes the same processing as S004 to S009 in FIG. 4.

In the following S111, the control circuit 2 subtracts the Vref measured in S103 from the Vtemp measured in S104, so that the increase in the anode voltage of the OLED 10 due to the leakage current corresponding to the temperature of the OLED 10 (ΔVtemp ) Is calculated.

Next, in S112, the control circuit 2 calculates the temperature based on the ?Vtemp calculated in S111. The temperature calculation in S112 is performed by applying the ΔVtemp calculated in S111 to the conversion equation or conversion table between ΔVtemp and temperature obtained experimentally in advance.

Next, in S113, the control circuit 2 checks whether or not the temperature calculated in S112 is within a certain range, and if the former is outside the latter range, it does not correct the gradation voltage and terminates the process as it is, and the former is within the latter. If so, the process proceeds to S114. Here, within a certain range is within a range of a temperature that may be the temperature of the environment in which the electro-optical device is used. If it exceeds that range, since an abnormality has occurred and correction of the gradation voltage is almost meaningless, the processing is stopped.

In S114, the control circuit 2 determines the pre-deterioration voltage-current characteristic corresponding to the temperature calculated in S112. The determination of the voltage-current characteristic in S114 is performed by obtaining the shift amount by applying the temperature calculated in S112 to the conversion equation between the temperature and the Voled shift amount obtained experimentally in advance or the conversion table.

In the following S115, the control circuit 2 corresponds to the gradation voltage (Vgs=Vdata-Vref-Vth) on the characteristic curve of the voltage-current characteristic determined in S114, and the current Ioled1 supplied by the driving transistor 11 Determine the Voled (reference value) of. Specifically, the current Ioled1 supplied by the driving transistor 11 is calculated in response to the gradation voltage (Vgs=Vdata-Vref-Vth) programmed for the target OLED, and shipped as a corresponding current Ioled1. The shift amount determined in S114 is subtracted from the Voled experimentally obtained at the time. In the example of Fig. 24(b), the solid line represents the voltage-current characteristic curve when the OLED before deterioration is operated at room temperature, and the dashed line is the predicted voltage as that of the OLED before deterioration at the temperature calculated in S112. -It shows the current curve.

In the following S116, the control circuit 2 calculates a Voled actual measurement value by subtracting the Vsense measured in S103 from the Vsense measured in S109 and adding the known Vref as shown in Equation 6 below.

In the example of Fig. 24(b), the broken line represents the voltage-current curve predicted as that of the OLED after deterioration at the temperature calculated in S112.

In the following S117, the control circuit 2 compares the measured Voled value calculated in S116 with the reference value determined in S115, and calculates the difference ?V between the two. In the example of Fig. 24B, it is calculated by ΔV = Voled3-Voled2.

In the following S118, the control circuit 2 determines the current-luminance characteristic after deterioration corresponding to ?V. Here, since there is a correlation between the amount of change in the voltage-current characteristic and the amount of change in the current-luminance characteristic due to the aging deterioration of the OLED 10, the control circuit 2 is based on ΔV, and the current after deterioration -This is because the inclination of the luminance characteristic straight line from the inclination angle before deterioration can be calculated.

In the following S119, the control circuit 2 determines the correction relationship of Ioled based on the difference in the slope of the current-luminance characteristic before and after deterioration. This correction relationship can be expressed as a ratio because the degradation of the OLED represents the difference in the slope of the current-luminance characteristic.

In the following S120, the control circuit 2 determines a gradation correction function based on the correction relationship determined in S119.

In the following S121, the control circuit 2 determines the grayscale data of the next frame (all of the grayscale data input later when the processing of Figs. 20 to 22 is executed only when the process is started) by the above-described conversion coefficient. The correction is performed based on the conversion to the grayscale voltage and the grayscale correction function determined in S120. In addition, when the execution target row is one row at a time, the gradation voltage is corrected for the execution target row based on the gradation correction function determined in S120 during the processing of Figs. 20 to 22 this time, and the row other than the execution target row is If there is a gradation correction function determined in S120 during the processing of Figs. 20 to 22 performed in the past, the gradation voltage is corrected based on the gradation correction function stored in a memory (not shown). Otherwise, the correction Do not do. After completion of S121, the control circuit 2 ends the entire process of Figs. 20 and 22.

According to the second embodiment configured as described above, the temperature is calculated based on the leakage current of the driving transistor 11, and based on the calculated temperature, the voltage-current characteristics of the OLED 10 before deterioration at that temperature Since this is predicted and the difference ΔV between the voltage on the predicted voltage-current characteristic and the measured value is calculated, malfunction due to temperature is reliably prevented.

<modification example>

This second embodiment is an electro-optical device using an OLED element whose current-luminance characteristic does not change depending on temperature, but even if it is an electro-optical device using an OLED element whose current-luminance characteristic varies depending on temperature, As in the second embodiment, if the correlation between the current-voltage characteristic and the current-luminance characteristic at each temperature before deterioration and the current-voltage characteristic and the current-luminance characteristic at each temperature after deterioration is known in advance, the temperature and By measuring the Voled when a predetermined current is passed, correction is possible.

(Embodiment 3)

Fig. 25 is a circuit diagram of a drive circuit for each OLED 10 constituting the pixel circuit 1 of the electro-optical device according to the third embodiment of the present invention. Compared with the first and second embodiments described above, the present third embodiment does not include a circuit for compensating for Vth or β non-uniformity of the driving transistor 11. However, even when there is a Vth or β non-uniformity in the driving transistor 11, this non-uniformity appears as a change in the luminance characteristics of the OLED 10 in appearance, thereby compensating for the current-luminance characteristics caused by the aging deterioration of the OLED 10. There is no hindrance because it is compensated at the same time by executing the process.

In this third embodiment, other configurations and actions are the same as those of the first and second embodiments described above, and thus description thereof will be omitted.

(Embodiment 4)

Fig. 26 is a circuit diagram of a drive circuit for each OLED 10 constituting the pixel circuit 1 of the electro-optical device according to the fourth embodiment of the present invention. This fourth embodiment differs from the above-described first and second embodiments only in that the drain of the second scan transistor 17 is diode-connected to the second scan line S2, and a different configuration is used. We do it in common. Therefore, since the operation of the fourth embodiment is the same as that of the first and second embodiments described above, a description thereof is omitted.

<modification example>

In the above-described first to fourth embodiments, all of the transistors are composed of a P-channel MOSFET, but it goes without saying that the necessary modifications may be made by constituting an N-channel MOSFET.

1: pixel circuit 2: control circuit
10: OLED 11: driving transistor
14: initialization transistor 16: sensing transistor
17: third transistor 21: grayscale data correction operation unit
22: gray voltage generator 23: reference voltage supply circuit
24: voltage detection unit 25: scan signal generation unit
32: second capacity D: data line
P: 1st power line S1: 1st scanning line
S2: second scan line

Claims (12)

An electro-optical device that emits light with a luminance corresponding to the gradation data by supplying a driving current corresponding to a gradation voltage based on input gradation data to the light emitting element,
It is electrically connected between a power source and an electrode of the light emitting element, the gray voltage is selectively applied to the gate, and when the gray voltage is applied to the gate, a driving current corresponding to the applied gray voltage is applied to the light emitting element. A first transistor to supply;
A second transistor having a gate electrically connected to the electrode of the light emitting element and a source or drain electrically connected to a circuit including a voltmeter;
In a state in which the gray voltage is applied to the gate of the first transistor, the measured value of the voltmeter is read, and the gray voltage applied to the gate of the first transistor is then corrected based on the measured value. Control circuit; And
And a third transistor selectively applying a reference voltage to the electrode of the light emitting device,
The control circuit, in a state in which the third transistor is controlled to apply the reference voltage to the electrode of the light emitting element, reads the measured value of the voltmeter as a first measured value, and reads the measured value of the first transistor to the gate of the first transistor. In a state in which the third transistor is controlled so as not to apply the reference voltage to the electrode of the light emitting device while applying the gray voltage, the measured value of the voltmeter is read as a second measured value, and the first measurement An electro-optical device, characterized in that, based on a difference value between the value and the second measured value, the gray voltage applied to the gate of the first transistor is then corrected. delete The method of claim 1,
An electro-optical device, characterized in that: a reset voltage is selectively applied to the gate of the first transistor, and when the reset voltage is applied to the gate of the first transistor, the control circuit reads the first measured value. . The method of claim 1,
The electro-optical device, wherein the plurality of light-emitting elements are provided, and each light-emitting element includes the first and second transistors. The method of claim 3,
The reset voltage, the gradation voltage, and the reference voltage are supplied from the control circuit through a common data line. The method of claim 5,
And a circuit including the voltmeter is electrically connected to the second transistor through the data line. The method of claim 6,
A first scan transistor controlled by the control circuit to intercept between the data line and the gate of the first transistor, and a second scan transistor controlled by the control circuit to open and close the circuit including the voltmeter. Electro-optical device comprising the. The method of claim 3,
And a capacitor electrically connected between the gate and the source of the first transistor to maintain the reset voltage or the gradation voltage. The method of claim 1,
The control circuit, when applying the gradation voltage to the gate of the first transistor, uses a voltage generated at the electrode of the light-emitting element before deterioration due to a current supplied to the light-emitting element by the first transistor as a reference value, And correcting the gradation voltage applied to the gate of the first transistor according to a deviation between the reference value and the difference value. An electro-optical device that emits light with a luminance corresponding to the gradation data by supplying a driving current corresponding to a gradation voltage based on input gradation data to the light emitting element,
Electrically connected between a power source and an electrode of the light emitting device, the gray voltage or reset voltage is selectively applied to the gate, and when the gray voltage is applied to the gate, a driving current corresponding to the applied gray voltage is applied. A first transistor supplied to the light emitting device and turned off when the reset voltage is applied to the gate;
A second transistor having a gate electrically connected to the electrode of the light-emitting element and a source or drain electrically connected to a circuit including a voltmeter and a power source; And
In a state in which the reset voltage is applied to the gate of the first transistor, the measured value of the voltmeter is read as a temperature measured value, and the gradation voltage is applied to the gate of the first transistor, the voltmeter The measured value of is read as a voltage measured value, the voltage measured value is corrected based on the temperature measured value, and the gradation voltage applied to the gate of the first transistor is then applied based on the voltage measured value. An electro-optical device comprising a control circuit for correcting. The method of claim 10,
Further comprising a third transistor for selectively applying a reference voltage to the electrode of the light emitting device,
The control circuit, in a state in which the reset voltage is applied to the gate of the first transistor, reads the measured value of the voltmeter as a third measured value, and applies the reset voltage to the gate of the first transistor. And, in a state in which the third transistor is controlled to apply the reference voltage to the electrode of the light emitting element, the measured value of the voltmeter is read as a first measured value, and the gate of the first transistor is In a state in which the third transistor is controlled so as not to apply the reference voltage to the electrode of the light emitting device while applying the gray voltage, the measured value of the voltmeter is read as a second measured value, and the first measurement The gray scale to be applied to the gate of the first transistor, based on the difference value, calculating a difference value between a value and the second measurement value, correcting the difference value based on the third measurement value Electro-optical device, characterized in that for correcting the voltage. The method of claim 11,
The control circuit measures the third voltage generated at the electrode of the light-emitting element before deterioration due to a current supplied by the first transistor to the light-emitting element when the gray-scale voltage is applied to the gate of the first transistor. A value shifted based on a value is used as a reference value, and the gradation voltage applied to the gate of the first transistor is then corrected according to a deviation between the reference value and the difference value.

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